The objective of this study is to assay soluble antigen-antibody complexes in serum of patients with breast cancer using C1q binding radioimmunoassay, Raji cell radioimmunoassay, and (rabbit) rheumatoid factor assay. The serum specimens will be obtained from breast cancer patients, fibrocystic breast disease patients and breast cancer families as well as from appropriate healthy control individuals. The breast cancer patients will be longitudinally followed for evaluation of the response to treatment in order to determine the prognostic and monitoring values of the assay. The high risk groups (fibrocystic breast disease and breast cancer families) are also to be followed in order to evaluate the diagnostic potential of the immune complex assay. The antigen-antibody complexes are also to be isolated from the serum and body fluids (pleural effusion) of breast cancer patients by molecular exclusion chromatography, protein A affinity chromatography and immunoadsorption using affinity media to the Fc domain of IgG. Further, the isolated immune complexes will be dissociated under the least denaturing conditions. The dissociated antigens are to be characterized biochemically and immunologically. Xenobiotic antisera will be raised with the dissociated antigen(s) and with isolated complexes as well as with the Raji cells containing surface-bound immune complexes injected into rabbits made tolerant to human IgG, and studied by their ability to recombine the dissociated antigen and to bind malignant breast tissues. In vitro antibody-dependent cell-mediated cytotoxicity, lymphocyte mitogenesis, PHA-induced lymphocyte blastogenesis and LAI assays are also to be performed to study the possible biological function of antibody-antigen complexes. Further, a radioimmunoassay will be developed which may be of use in early detection and monitoring of efficacy of therapy for breast cancer.